A wireless communication system, according to the path for communication between a source and a sink, may include a network for directly communicating between the source and the sink, e.g. a cellular network, or a network for communication between the source and the sink via a relay node, e.g. a relay network and a mesh network.
Because the source can directly communicate with the sink, the cellular network may be referred to as a single-hop network, and the network with the relay node is referred to as a multi-hop network.
The single-hop network only includes a Base Station (BS) and a Mobile Station (MS). When uplink bandwidth is allocated, it is necessary only to allocate the bandwidth between the BS and the MS, thus the allocation method is simple. However, the multi-hop network not only includes a Mobile Multi-hop Relay BS (MMR-BS) and an MS, but also includes a Relay Station (RS). The RS has resource scheduling capability, and may acquire node topology information within its own administration range, send a resource scheduling broadcast message, and serve as a synchronous station of other nodes.
FIG. 1 is a schematic diagram illustrating the structure of a typical multi-hop network. As shown in FIG. 1, the multi-hop network includes one MMR-BS, six RSs and four MSs. By taking the leftmost branch as an example, the access station of MS1 and MS2 is RS2; the synchronous station of RS1 is RS3; the synchronous station of RS3 is an MMR-BS; the link between MS1 and RS2 is an access link; the links between RS2 and RS1, between RS1 and RS3, and between RS3 and the MMR-BS are relay links; the link between the MMR-BS and MS1 is a multi-hop link.
In the multi-hop network, there are two resource scheduling methods; one is a centralized resource scheduling method, and the other is a distributed resource scheduling method.
The centralized resource scheduling method includes: the MMR-BS is responsible for centralized allocation of the relay link bandwidth and the access link bandwidth, and the RS has no right of bandwidth allocation. Because the MMR-BS needs to allocate bandwidth for all links, the processing of the MMR-BS is very complex and the RS needs to report detecting results of the links in real time. If the number of link hops is large, the time interval from allocating bandwidth for a link to transmitting data by using the link is large, and the link condition may change during the time interval; in this way, the allocated bandwidth is inapplicable to the changed link condition, which will impact the data transmission.
The distributed resource scheduling method includes: the MMR-BS is responsible for the bandwidth allocation for the link between the MMR-BS and its own next hop node, and the RS is responsible for the bandwidth allocation for the link between the RS and its own next hop node. The disadvantage of the centralized resource scheduling method that the processing of the MMR-BS is very complex may be reduced in the distributed resource scheduling method. However, even if the resource scheduling function of the MMR-BS is independent of that of the RS, the delay of data transmission is still big. As shown in FIG. 2, the MMR-BS, RS1 and RS2 all can independently allocate bandwidth for their respective subordinate nodes; after acquiring the bandwidth, the subordinate nodes transmit data to their respective superordinate nodes. For example, RS2 first allocates bandwidth to an MS, the MS transmits data to RS2 using the allocated bandwidth; RS2 acquires bandwidth from RS1 after a long time, and transmits data to RS1; RS1 acquires bandwidth from the MMR-BS after a long time, and transmits data to the MMR-BS. Therefore, if the resource scheduling function of MMR-BS is independent of that of the RS, the delay of data transmission will be big. The MMR-BS and the RS allocate bandwidth for their respective subordinate nodes by a bandwidth grant method.
A distributed scheduling method based on a whole link mechanism is proposed at present in order to overcome the problem of data transmission delay in the distributed resource scheduling method, and includes: the MMR-BS and each RS allocate bandwidth for their respective subordinate nodes in turn; when an MS transmits data, the MS and each RS have acquired the bandwidth, thus the MS can rapidly transmit the data in the uplink until the data arrives at the MMR-BS.
The distributed resource scheduling method based on a whole-link mechanism can overcome the delay of data transmission. However, because bandwidth of all links is allocated before the MS transmits data, the time interval from allocating bandwidth for a link to transmitting data by using the link is large if the number of link hops is large. For example, a link includes the MMR-BS, RS2, RS1 and the MS; the MMR-BS first allocates bandwidth for RS2; RS2 allocates bandwidth for RS1; RS1 allocates bandwidth for the MS; the MMR-BS, RS2 and RS1 wait for the data transmitted by their respective subordinate nodes after allocating the bandwidth for their respective subordinate nodes; the MS directly transmits data to the MMR-BS via RS1 and RS2 using the allocated bandwidth. That is to say, after the bandwidth is allocated for each node, the time for transmitting data from the MS to the MMR-BS is reduced, but at the cost of the long waiting time of the MMR-BS and each RS. Therefore, the time from allocating bandwidth to transmitting the data completely is still long. However, because the MMR-BS and each RS allocate bandwidth for their respective subordinate nodes in advance, the link condition may also change during the waiting time for the data transmission; in this way, the allocated bandwidth may be inapplicable to the changed link condition, which will impact the data transmission.